Is it possible to exchange value for value without the use of currency? When most trades take place currency is not used at all. These kinds of transactions are the most common but they are deemed not to exist in economics dogma.
When a candidate runs for office voters offer support in return for the expectation of representation. Cash does not change hands. This is part of the market for representation. In the absence of any other influence, value is exchanged and voters have the representation they expect in return for support.
But, the market for representation is ongoing. Voters are outbid immediately and their expectation of representation disappears as soon as the candidate is offered more value. Representation does not stay with voters who offer only support. Candidates are offered greater value with both non currency transactions and outright cash in terms of financial support.
In the game of government all interaction is based on self interest. If the self interest on two are more entities is in question there are only two options. The different parties can come to an agreement. That is a free market outcome, The other option is the use of coercion, which can be expressed as outright force through violence.
After voters are outbid with respect to representation, they do have the choice of using coercion as in removing the representative or using fear of removal to regain their lost representation.
Voters are seldom aware that they have been outbid.